This invention generally relates to a remotely operable clamp for attachment to a member disposed in a subsea environment, and more particularly relates to a remotely operable clamp utilizable with cathodic protection anodes or anode pairs to be attached to the submerged or subsea portion of a large metal structure, such as a drilling rig, production platform or pipeline. In addition, the clamp may be utilized in other subsea operations, such as salvage or pipeline repairs.
The offshore oil and gas industry utilizes many offshore subsea structures, such as offshore drilling platforms, offshore production platforms, well platforms, pipelines and other metal structures, all or the greatest portion of which are submerged in a subsea environment, and the majority of which are steel. All of these structures are provided with cathodic protection systems to safeguard the submerged metal surfaces of the structures in contact with the corrosive electrolytic subsea environment. The vast majority of the cathodic protection systems (probably better than 90%) are of the galvanic or sacrificial type, which means that electropositive metal alloys (mainly aluminum or zinc) that act as the anodes in the cathodic protection system are electromechanically attached to the subsea portions of the structures and are electrochemically sacrificed over long periods of time. The life of these systems is finite, and the anodes have to be replaced periodically, often in a time span of 10 to 15 years. Currently, replacement of the anodes on an off-shore structure have a number of problems associated therewith:
1. The installation costs of the replacement anodes are high because divers must be used to replace the anodes;
2. In deep waters the installation costs can become prohibitive due to the increased cost of the dive-time, including the extremely high cost of diver insurance to protect against the risks of injuries to the divers; and
3. Underwater welding techniques have not yet progressed to a point where an acceptable structural weld can be made on offshore structures in a subsea environment. Therefore most of the anode replacement systems must be clamped to the structure mechanically using fully-encircling clamps. On many large structures, where several hundred anodes must be replaced at one time, the diver time required to replace the anodes and use fully-encircling clamps drives the replacement cost to almost prohibitive levels.
The prior art in replacing anodes has been mainly confined to diver installed fully-encircling clamps. However, one major oil company has recently experimented with the use of remotely operated submersible vehicles (ROV's) by using a "ram set" explosively fired pin that secured a saddle to a subsea structural member of the structure to be protected. The pins actually penetrated the metal tubular member. The replacement anodes were attached by means of cables to the saddle and hung suspended by cable from the secured point on the structure. However, due to the fact that the full extent of potentially irreversible damage to the structural members has not yet been fully explored and defined, this technique is not generally considered satisfactory and has not gained acceptance.
The diver installed clamps that are presently in use for attaching anodes to the subsea portions of offshore structures suffer several serious disadvantages:
1. The fully-encircling devices such as "U"-bolts or semi-circular bolted clamps, require diver manual manipulation, positioning and attachment, and therefore are not convertible to diver-free installation by a remotely operated submersible vehicle or ROV;
2. The fully-encircling clamps are difficult to rig into position because they are bulky and hard to handle in a subsea environment, and hence are very time consuming to install; and
3. Since the fully-encircling clamps often have trouble penetrating any marine growth on the metal structural member, a set-screw must be utilized between the clamp and the metal structure to provide electrical continuity. Alternatively, a weld must be provided between the clamp and the metal struture. However, because of marine growth, the set-screw arrangement does not always provide good electrical continuity, and welding, which would be the most reliable form of providing electrical continuity, is frequently not possible because of the structure and the state-of-the-art of the technology, the marine growth and the location of the attaching point for the anodes.